Branch sap flow in a mature olive tree: dynamics and relation to architectural traits

This study examined how sap flow in shoots and branches of a mature olive tree (Olea europaea ‘Coratina’) related to morphological traits which are linked to tree hydraulic architecture. Spatial and temporal variations of sap flow within the tree canopy were investigated; they were analyzed with respect to the ratio between sapwood area and leaf area (SA/LA), and in relation to evaporation demand. The work was carried out on distinct sets of sap flow data, collected using different thermal methods (Heat Field Deformation - HFD and Stem Heat Balance with external heating – SHB). Sap flow density (q) appeared to be governed largely by the ratio SA/LA, irrespective of the strength and heterogeneity of the evaporation demand that affected the tree water loss. The relationship between q and SA/LA suggested a higher efficiency of the water supply pathway when SA/LA was lower, i.e. in smaller (and more distal) branches.